Q. 515.0( 1 Vote )

# If the focus of a parabola is (0, –3) and its directrix is y = 3, then its equation is

A. x^{2} = –12y

B. x^{2} = 12y

C. y^{2} = –12x

D. y^{2} = 12x

Answer :

As focus lies on y – axis,

Equation is x^{2} = 4ay or x^{2} = -4ay,

Focus has a –ve co = ordinate, so equation is x^{2} = -4ay,

Co – Ordinate of focus = (0, -a)

-a = -3

a = 3

As per the equation,

x^{2} = -4ay

x^{2} = -4 (3) y

x^{2} = -12y

Hence, the required equation is x^{2} = -12y.

Option (A) is the answer.

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